Bike pulling way too much to the left.

So I just recently finished putting my 73 Commando back together after I had it's frame powder coated. I took it to a shop that specializes in Nortons and had them give it a once over to make sure I did everything correctly. Well, I didn't. I installed both the front and rear isolastics with the adjsters on the right side of the bike. I didnt realize they were supposed to be opposite each other. Instead of reversing the rear isolastic, we just reversed the front one. Now my question is that the bike pulls wayyy too hard to the left. It's very unstable. The mechanic seems to think it's because I have too small of a tire on the front wheel. Could that be the case, or is it that we have the isolatics in backwards? Or is something completely different that I might have messed up on during the build.

There are so many things that can affect the handling and straight running of a Commando that it's almost mentally exhausting to contemplate. If this helps my 76 was rebuilt by the P.O. after powder coating , and both sets of vernier iso's now are adjustable on the timing ( right) side. Runs true though. Loads of searchable info on the site on this...

msh5337,
If its pulling to the left then check your rear wheel that it is tracking with the front. Look for obvious signs like length of chain tension bolts on each side or that the axle spindle is making contact on these chain tension stop bolts. No air gaps. Check the rear tire is equal distance between the swing arm on each side. Try placing a straight length of bar contacting the rear wheel tire outside edge and see how it lines up with the front tire when it is centered.
Cheers,
Thomas
CNN

The first thing that came to mind is: Are the wheels in line? It's all too easy to get them out of line.

If they are not in line, then correct this first. The front wheel rim should be centralised in the front fork. If not, you will have to rebuild it with the correct offset. Then check the wheel alignment. You can use string, lasers or long, straight bits of wood, steel, neon lights, etc.

The rear wheel is also 'dished', but less so that the front. The rear wheel rim offset with its hub could be correct but it could still be out of line with the front.

Search this site to get the correct rim: hub offset data.

You should also check that the rear wheel is not cocked in the swinging arm. Mine was. Also, when I first got my Commando, the wheels had been built incorrectly so the rear was way of out of line with the front. The rear mudguard obscured the view but when that was removed, it was plain to see that the rear wheel was both out of line and cocked in the swinging arm. One arm of the fork was higher than the other and one of the wheel spindle lugs was bent.

It could be that the entire engine/gearbox/swinging arm sub-assembly is cocked with reference to the horizontal axis of the frame.

If just the rear wheel is not parallel with the front, it will appear easier to steer in one direction than the other. It could even be that both wheels are off line from the centre line of the frame.

Something's not right with the geometry so you will have to check by a process of elimination what the problem is.

Apologies if you have already checked and are confident of the above. Otherwise, you have some homework to do!

Let us know how you get on.

Dave

Okay, great. Thanks for the info everyone! Makes me feel better that it's not the isolastics. I'll check out the front and rear wheel. It's very possible that I have it cocked a bit in the swing arm. I just didn't think that that would cause THIS big of a difference in handling. Turning to the left is just fine, but any right hand turn is extremely sketchy. Felt like I was going to drop it once or twice on the test ride.

Take the time to correct your isolastics. The bike's swingarm is mounted on the cradle which is held in the place by your correctly assembled isolastics. The isolastic assembly is suposed to locate the swingarm so it's aligned within the frame, and insure the plane of the swingarm's path of travel is aligned with the steering head... If you don't have that situation to start with, you wheels may not be in the same plane, so any linear alignment you make to the rear wheel will not create a planar alignment...

Fix what you know is wrong, then go from there.

msh5337 said:

I installed both the front and rear isolastics with the adjsters on the right side of the bike. I didnt realize they were supposed to be opposite each other. Instead of reversing the rear isolastic, we just reversed the front one. Now my question is that the bike pulls wayyy too hard to the left.

Click to expand...

I assume you mean vernier Isolastic kit "adjusters"?

If it is the pre-Mk3 front vernier conversion kit, then it shouldn't matter which side the front (or rear) adjuster is, as the fixed abutment and adjuster are the same width so there was no need to change the front adjuster from right to left although according to Oldbritts it should be on the right side.
http://www.oldbritts.com/13_067337.html

However, if it's the vernier conversion that uses the Mk3 Isolastic parts and modified front mount, then the FRONT adjuster must go on the RIGHT side.
With the Mk3 adjuster on the LEFT (and fixed abutment on the right) it would pull the cradle assembly out of alignment as the Mk3 front adjuster and fixed abutment are different widths.

http://www.oldbritts.com/13_067116.html

To be accurate with rear wheel alignment I use a large set of dividers and measure to the center of the axle to the center of the isolastic spindle, using the idea that the iso spindle must be parallel to the swing arm spindle must be parallel to the rear wheel spindle. The swingarm spindle is very hard to get to on the left side so I use the iso spindle. Usually I will put the spindle and axle in a lathe and put in a small dimple which improves accuracy. This method works very well.

I use two long straightedges as high up under the machine as will go and measure to the wheel rims, front and back of each rim and both sides, not the tires. For modern machines with smaller width front wheels, when the straightedges are parallel to the rear rim and equidistant on both sides of the rear rim, the 4 measurements at the front should be the equal and minus half the difference in wheel width. If this could be done at axle height, it would be dead-nuts accurate. As is, is gets pretty close.

So if both wheels are made parallel and the measurements are different on either side of the front, the rear axle needs to be adjusted on one side and checked again. If the front numbers are smaller on the left, the rear wheel is cocked to the right and vice versa. This eliminates fussing to get the front wheel exactly centered.

Incorrectly-laced wheels are another problem that should be addressed before making an attempt at alignment.

+1
That's the method I've had the most success and "least" hassle with when initially setting up a bike. I use 8 foot florescent tubes on bare rims. The tubes are quite straight, cheap, readily available, and I haven't broken one yet (knock knock). I gave up trying to tell when a string is JUST touching the front edge of the rear rim.
Bill

Another quick check for the rear wheel alignment in the frame is to look at the drive chain and how it runs on the sprockets.
While slowly turning the rear wheel look at how the top chain run moves toward the drive sprocket.
Should be a straight run of course.

If the bike handled fine before you swapped the ISO adjuster over just put it all back where it was. Or am I missing something?

Dave

Dave,
That's exactly what I was thinking, but didn't want to be accused of stating the bloody obvious!!
Martyn.

Did you check to see that the frame was straight when it was apart ?

Greg

Hey Pantah good to check the string at the back wheel I use a cigarette paper. Just like using a feeler gauge.

Yep, that would work, I like it.

I rode for years on a Commando with a parallelogramed frame, the rear wheel was not vertical giving interesting wheel alignment problems. The giveaway was that the front iso bolt didn't want to poke through the LH frame lug without some manipulation of the iso core spacer. Couldn't see any obvious misalignment but it was bent.

msh5337 said:

Okay, great. Thanks for the info everyone! Makes me feel better that it's not the isolastics. I'll check out the front and rear wheel. It's very possible that I have it cocked a bit in the swing arm. I just didn't think that that would cause THIS big of a difference in handling. Turning to the left is just fine, but any right hand turn is extremely sketchy. Felt like I was going to drop it once or twice on the test ride.

Click to expand...

I suggest you don't assume the isos are beyond reproach. This is what I meant by the possibility that the engine/gearbox/swinging arm assembly is cocked in relation to the centre line of the frame.

If only right handers feel bad, then it sounds like one wheel is way out of alignment with the other, or even both wheels are over to one side of the centre line of the frame.
As some of the previous posters remarked, when was the last time the bike handled properly? Before the isos were replaced?

Thanks for the help so far everyone. Sorry for resurrecting this thread, but I'm still having this problem. Both isos have been placed in the correct position, but it didn't help. I finally broke down and took it back to the mechanic. He still swore up and down that it was the front tire causing the problem. He switched the front wheel out with the one from his Commando and said that it ran true. Said that if I changed my front tire all should be well. Well, i had an Avon Roadrider put on by a shop today and it didn't fix it!!!! I'm losing my mind. Could the wheel be that bad out of true that it's causing it to pull to the left? Surely the shop that replaced my tire would've noticed that right?

The front wheel would wobble obviously if it was out of true. It may however not be centred correctly in the forks, simply put two fingers either side of the tire and forl leg and see if there is a difference in the gap, this can be quite easily rectified on the bike with a spoke spanner and a little patience. A tyre- fitter would probably not notice if the wheel was out of true and would certainly not know if the rim was correctly centered.

I would ask your mechanic to put his own front wheel in and let you ride it to see if it makes any difference. That way you would know for sure you are looking in tne right place.

The width of front tyre or brand should make no difference to the bike having a left or right biase.

Have you checked your swing arm bushes by grabbing the rear wheel and trying to move it sideways? The centre pin can wear the bore in the gearbox an oval shape over time and the small retention bolt at the top simply acts as a fulcrum once this sets in.